Australian customs officers discovered the drugs after conducting an x-ray of their baggage. The bags were found to contain 36 green bottles labelled as sparkling water, but after tests officers said the bottles proved to be liquid methamphetamine, commonly known as the drug ice, which has a booming market.

Australian Federal Police arrested and charged a 63-year-old man and 54-year-old woman with importing commercial quantities of border controlled drugs.

The pair were due to appear in Central Local Court in Sydney on Friday, with the charges carrying a maximum penalty of life imprisonment.

Australian Border Force acting regional commander for New South Wales Tony McSweeney said the drugs haul another example of force's ability to stop drugs being smuggled into Australia.

He said: "This is not the first time this year and I'm sure it won't be the last where ABF officers at Sydney International Airport have managed to stop a large quantity of illicit drugs reaching the streets."

Liquid meth in bras

Simone O'Mahony, the Australian Federal Police's Acting Sydney Airport Commander, added that their members at the airport were continually surprised at how far people would go to import drugs.

She added: "What they don't realise is these attempts to smuggle in illicit substances can and do come to the attention of law enforcement. And we are ready to apply the full force of the law in response."

Last February Australian police made one of the country's biggest ever drug busts seizing more than Aus$1bn (£500m, US$644m) in methamphetamine concealed as gel inserts for bras.

The recent report by the Australian government showed that the use of the highly addictive drug had doubled since 2007 to more than 200,000 users in 2013, with anecdotal evidence of higher current numbers.

Also, a separate Australian crime commission report published in 2015 found that while $80 bought one gram of ice in China, users in Australia had to pay US$500 for the same amount.